Citta (loosely translated as mind) is nothing but consciousness in its functioning state. Heart (not the physical here) is thecenter of the consciousness. Electricity flows throughout the network of the wires but for any application it is available in the socket (outlet) where we plug in our gadgets. Similarly, consciousness is all pervading but a yogi can bring his awareness to the subtle heart (according to some, the anahat-cakra) and by performing Samyama on that can get the knowledge of Citta. This way he gets the knowledge of the nature of the mind. Needless to say one who masters the mind, masters everything in this universe.